1. Field of the Invention
The present invention relates to a band feeding and tightening system in a strapping machine for automatically feeding a band to an arch guide and tightening the band guided in a looped condition along the arch guide around a package by using a return roller and a feed roller contacting each other.
2. Description of the Prior Art
As one of the conventional band feeding and tightening apparatus, it has been proposed to use an apparatus disclosed in Japanese Utility Model Publication No. 23280/1965, in which a return roller and a feed roller rotated at a high speed in the reverse direction of each other are disposed in spaced relation and rocker rollers are provided to selectively contact with the rollers respectively so as to feed the band at a high speed or to tighten the band and a tension lever is provided to impart strong tightening torque to the band. In Japanese Unexamined Publication No. 64396/1977 proposed as an improvement of the conventional apparatus, the tension lever is omitted.
The construction will be illustrated referring to FIGS. 5 and 6.
Rocker rollers (40) and (41) are contacted with a feed roller (42) under pressure and a band is fed into an arch guide (43). The free end of the band passing through the arch guide in looped shape is contacted with a limit switch actuator (44) under a slide table (5) to deenergize a solenoid (45) so as to disengage each rocker roller (40), (41) from the feed roller (42) whereby the feeding operation is completed. Then, a light gripper (48) is raised through a group of cams (47) by the rotation of a seal forming shaft (46) to grip the free end of the band with association of the slide table (5).
After this, the rocker roller (49) is contacted with the return roller (50) under pressure by energizing the solenoid (56) to pull the band back. When the tightening force is reached to a specific value the clutch begins to slip to decrease rapidly the revolution speed of the return shaft (52). When the revolution speed is lower than that of a sprocket (53), the rotation of the sprocket (53) which has not effected the function, is effectively transmitted to the return shaft (52) whereby the band is further tightened by the return roller (50) of the return shaft (52) depending upon low revolution speed under high torque which is imparted to the sprocket (55) of the differential reducing machine (20).
The other conventional apparatus for feeding and tightening the band by rotating a single roller in the positive or the reverse direction has been proposed. However, its rotation should be low in order to impart a strong tightening torque to the band for the attainment of the final tightening thereof. Therefore, it does not satisfy the demand in the field of the strapping machine which increasingly requires to shorten the time for strapping. In the conventional system, the band is often run over from the guide or is bent in the guide because the force applied to feeding the band by the rotation of the single roller is disadvantageously too great during the feeding operation.